Face perception is important for recognizing others and their thoughts. For example, we can easily recognize identities and intentions of individuals although faces have similar visual features to each other. How can we do it? Previous studies suggest that the Fusiform Face Area (FFA) is important for face perception because it responds selectively to faces. Current study investigated FFAs of 10 epileptic patients. Specifically, we measured the effect of electrical stimulation of FFA on face categorization and how the effect of stimulation varied depending on the signal strength of face stimuli. We first defined face-selective area around FFA by using both anatomical and neurophysiological criteria. For the anatomical criterion, we first found Talairach coordinates of the implanted electrodes by MR-CT co-registration and then compared them to the FFA coordinates of previous researches. When the Talairach coordinates of our electrodes were within FFA coordinates of previous researches, we considered these electrodes as face-selective. We analyzed the magnitude of face-selective component (N200) for the neurophysiological criterion. When electrodes showed significantly larger N200 component to faces than to scenes, we defined these electrodes as face-selective. After categorization of electrodes depending on the two criteria, we measured face-categorization thresholds with electrical stimulation and compared them to those without stimulation. Face categorization thresholds with stimulation were increased only when both the anatomical and the neurophysiological criteria were satisfied, suggesting that electrical stimulation on face-selective area disrupted face perception. We also found that this disruption was compensated by increasing the visual signal of face stimuli. Our findings demonstrate a direct causal link between the face-selective area and face perception.

This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (No. M10644020001-07N4402-00110) to S.C. and partly by a grant (M103KV010016-08K2201-01610) from the Brain Research Center of the 21st Century Frontier Research Program funded by the Ministry of Science and Technology of the Republic of Korea to S.B.H.